With the rise of emerging services such as Video On Demand, high definition television, and online games, user's requirements for bandwidth grow increasingly, and the development of Fiber To The Home can effectively ensure the “Last Mile” access network bandwidth. A PON system is one of the most widely applied Fiber To The Home technologies at present.
FIG. 1 is a schematic diagram of the constitution of a PON system and the position of the PON system in a conventional network architecture. The PON system mainly includes an OLT (Optical Line Terminals), ONUs (Optical Network Units), an optical splitter, and an ODN (Optical Distribution Network). The OLT and the optical splitter are connected to each other through a trunk fiber, and the optical splitter implements point-to-multipoint optical power distribution and is connected to multiple ONUs through multiple branch fibers. The trunk fiber, the optical splitter, and the branch fibers between the OLT and the ONUs are collectively referred to as the ODN. The direction from the OLT to the ONUs is referred to as a downlink direction, and the direction from the ONUs to the OLT is referred to as an uplink direction.
In the conventional PON system, the split ratio of the optical splitter ranges from 1:16 and 1:32 to 1:64 with a maximum of 1:128 which is optional. The OLT is connected to few ONUs through the optical splitter and has a covering radius of not more than 20 km, so that a large number of OLTs exist in the conventional network architecture and are located in remote areas in a dispersed manner, resulting in inconvenience in administration and maintenance and high device investment and maintenance cost. The reach extension of the PON can simplify network layers such as an access layer and a convergence layer, reduce the number of network nodes, increase the number of users connected to a single OLT, apportion the cost to a large extent, and finally reduce device investment and save administration and maintenance cost.
A basic architecture of an LR-PON (Long Reach PON) is as shown in FIG. 2. An RE (Reach Extension device is placed between an optical splitter and an OLT, and the RE device may be in an electrical relay manner or an all-optical relay manner. After the RE device is added, the conventional ODN network is divided into two ODN networks, namely, ODN1 and ODN2. In the all-optical relay manner, the all-optical RE device implements a function such as amplifying an optical signal.
The basic architecture of the LR-PON shown in FIG. 2 has the following problems.
1. An active RE device is introduced, and the stability and reliability of the entire ODN network are not as good as those of previous passive optical nodes.
2. The fiber transmission path is extended from the previous range of less than 20 km to a range of greater than 100 km, which introduces the fault probability of the long reach fiber path.
3. The coverage is expanded, and the number of users connected to the OLT is several to tens of times the previous one, resulting in wide range of influence on services caused by a fault.
4. With the addition of the RE device, the fiber path is divided into two or more segments, and if a segment of the path fails, the fault cause and fault point need to be located as soon as possible for processing without delay.
Due to the above several reasons, in the application of the LR-PON, the optical signal and the RE device per se need to be monitored and corresponding information such as alarm and performance needs to be generated, so as to implement functions, for example, protection and fault location. Therefore, it is necessary to establish a communication channel between the RE device and the OLT device to support the OAM (Operation, Administration and Maintenance) function for the RE device.
One solution for establishing the communication channel between the RE device and the OLT device in the prior art mainly includes: putting OAM information between the RE device and the OLT device in an uplink/downlink GTC (GPON Transmission Convergence) or GEM (GPON Encapsulation Mode) frame. In order to not affect the existing customer service, the line speed between the RE device and the OLT device may be increased, and the increased line speed may be used to accommodate the OAM information. The OLT and the RE device perform operations such as optical-electrical conversion, deframing/framing, and electrical-optical conversion to take out the OAM information from the GTC or GEM frame.
During the implementation of the present invention, the inventors find that this solution for establishing the communication channel between the RE device and the OLT device in the prior art at least has the following problem.
The line speed between the RE device and the OLT device needs to be increased, the existing PON system needs to be changed, and the solution is incompatible with the existing OLT device. The RE device and the OLT device have to perform the operations such as optical-electrical-optical conversion and deframing/framing to take out the OAM information from the GTC or GEM frame, so the processing is complicated and the cost is high.
Another solution for establishing the communication channel between the RE device and the OLT device in the prior art mainly includes: using a newly added wavelength different from wavelengths in uplink and downlink directions of the PON for establishing the communication channel between the all-optical RE device and the OLT device. OAM information between the RE device and the OLT device is transported through the communication channel established using the newly added wavelength.
During the implementation of the present invention, the inventors find that this solution for establishing the communication channel between the RE device and the OLT device in the prior art has at least the following problem.
The RE device and the OLT device need to process the newly added wavelength, so the implementation is complicated, great changes are made to the existing RE device and OLT device, and the device cost of the RE and OLT is increased.